10Be and U-Th dating methods for hydrogenetic ferromanganese nodules : preliminary results for examples from the Pacific Ocean and Tasman Sea

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Graham, I.J.; Ditchburn, R.G.; de Ronde, C.E.J.; Skinner, D.N.B.; Whitehead, N.E.; Wright, I.C.; Zondervan, A. 199910Be and U-Th dating methods for hydrogenetic ferromanganese nodules : preliminary results for examples from the Pacific Ocean and Tasman Sea. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 99/02 44 p.

Abstract: This report is the first output of a three year study of ferromanganese (Fe-Mn) nodule occurrences in the Campbell Plateau region of the New Zealand EEZ and UNCLOS claim region, South Pacific Ocean. Methods for dating Fe-Mn nodules using 10Be and U-Th isotopes, as developed at the Institute of Geological & Nuclear Sciences, are described and several different approaches to interpretation discussed. These include conventional linear or 2nd order polynomial models using 10Be concentration and/or 10Be / 9Be, and more novel models involving either background-reduced linear projections of 10Be concentration or 10Be / 9Be, or integrated 10Be / 9Be compared with theoretical curves. Analysis of six Fe-Mn nodules, two from the Tasman Sea and four from the Manihiki Plateau region northwest of the Cook Islands, yield dates ranging from 3 to 12 Ma, implying very slow growth rates in the order of 2-8 mm My-1. Such growth rates are typical of hydrogenetic Fe-Mn nodules worldwide. (auth)